South Korean activists on Saturday released huge gas-filled balloons filled with socks over the border into impoverished North Korea despite threats from Pyongyang.
The socks can be worn to help survive the harsh winter, be sold for cash or exchanged in the communist North for food that can keep a person going for a month, the campaigners say.
About 1,000 pairs of socks were launched by five large plastic balloons from the northern South Korean city of Paju.
Each pair of socks was attached with a leaflet containing a 'politically innocuous' message, said the Seoul-based group North Korea Peace, which has been sending socks to the North once a month over the past few months.
"We're not interested in sending political messages or sparking any troubles there. All we want is that people in the North wear warm socks over their frozen feet," Sunny Kim, a spokeswoman for North Korea Peace, told AFP.
"Warm socks are so rare and they can easily be traded for cash in the North. One pair of socks fetches about 22 pounds (10 kilos) of corn, which is enough to sustain a person for a month."
Socks and many other daily necessities are in short supply in North Korea, which pours money and resources into building up its 1.2-million-strong armed forces under its Songun, or military-first, policy.
Activists, many of them defectors from the North, regularly send leaflets over the border lambasting the regime and urging popular uprisings like those in the Middle East and North Africa in the past year.
The launches infuriate Pyongyang, which has threatened to open fire at launch sites.
Tensions have been high on the Korean peninsula since the conservative administration in Seoul rolled back the previous liberal government's "Sunshine Policy" of reconciliation and took a tougher stance toward Pyongyang.
Seoul also stopped its annual major food and fertiliser shipments to the North although it has been allowing humanitarian aid by civic groups, mostly modest in scale.
North Korea's leader Kim Jong-Il died on December 17 to be succeeded by his youngest son Jong-Un.
The North under its new leader has taken a hostile tone with the South's government, accusing it of failing to respect the mourning period for the late leader.